Frostbolt

Flash — Enchant Creature
When Frostbolt enters the battlefield, tap
enchanted creature. Enchanted creature doesn't
untap during its controller's untap step.
Enchanted creature has "At the beginning of
your upkeep, put two -1/-1 counters on this
creature." When Enchanted creature has four
-1/-1 counters on it, sacrifice Frostbolt.